eazing 0.0.1

The blazingly fast and mathematically optimized `easing functions` kit.
Documentation 
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use crate::easing::Curve;

use libm::{asinf, sinf};

/// The [`InSmooth`] Curve.
///
/// #### examples.
///
/// ```
/// use eazing::Curve;
/// use eazing::interpolation::polynomial::smoothstep::InSmooth;
///
/// let p = InSmooth.y(1.0);
/// ```
#[derive(Debug)]
pub struct InSmooth;

impl Curve for InSmooth {
  #[inline]
  fn y(&self, p: f32) -> f32 {
    let mut p = p;

    p = p.clamp(0.0, 1.0);
    p * p * (3.0 - 2.0 * p)
  }
}

#[test]
fn test_in_smooth() {
  let p = InSmooth.y(0.8);

  assert_eq!(p, 0.90450853);
}

/// The [`OutSmooth`] Curve.
///
/// #### examples.
///
/// ```
/// use eazing::Curve;
/// use eazing::interpolation::polynomial::smoothstep::OutSmooth;
///
/// let p = OutSmooth.y(1.0);
/// ```
#[derive(Debug)]
pub struct OutSmooth;

impl Curve for OutSmooth {
  #[inline]
  fn y(&self, p: f32) -> f32 {
    0.5 - sinf(asinf(1.0 - 2.0 * p) / 3.0)
  }
}

#[test]
fn test_out_smooth() {
  let p = OutSmooth.y(0.8);

  assert_eq!(p, 0.90450853);
}

/// The Non-linear Interpolation.
///
/// Interpolates smoothly between `min` and `max`. It will accelerated from the
/// start and deccelerated toward the end with a cubic easing.
///
/// #### params.
///
/// |      |                            |
/// |:-----|:---------------------------|
/// | `p`  | The progress.              |
/// | `x0` | The `min` start value.     |
/// | `x1` | The `max` end value.       |
///
/// #### returns.
///
/// `f32` — The interpolated result between the two float values.
///
/// #### examples.
///
/// ```
/// use eazing::interpolation::polynomial::smoothstep::smoothstep;
///
/// let p = smoothstep(0.25, 0.0, 1.0);
///
/// assert_eq!(p, 0.15625);
/// ```
#[inline]
pub fn smoothstep(p: f32, x0: f32, x1: f32) -> f32 {
  let mut p = (p - x0) / (x1 - x0);

  p = p.clamp(0.0, 1.0);
  p * p * (3.0 - 2.0 * p)
}